Field of the Invention
This invention relates to a stereoscopic microscope used, for example, for ophthalmic examination and having a Galilean type binocular stereoscopic microscope portion.
Description of the Prior Art
Heretofore, the Galilean type and the Greenough type optical systems have been widely used for the optical system of such a binocular stereoscopic microscope portion. In the Greenough type, entirely discrete two right and left microscopic optical systems are disposed so as to intersect each other at a predetermined angle, e.g. 10.degree.-12.degree. and therefore, the problem of convergence of eyes does not occur. In the Greenough type optical system, however, an objective, i.e. object glass is divided into two and therefore, for the purpose of magnification change, it is necessary to interchange the objective, and this leads to complexity and cumbersomeness. Also, the light beam is a convergent light and there is no portion in which the light beam becomes a parallel light beam and therefore, if an optical path dividing means is inserted to divide the optical path for a side view mirror or a camera from the intermediate portion of the lens barrel, the length of the optical path will be varied and thus, it is difficult to divide the optical path.
On the other hand, in the Galilean type, the optic axes entering the observer's eyes through eyepieces are parallel to each other and therefore, convergence must be effected as if an object actually perceived as lying nearby were at infinity. This leads to a disadvantage that it is difficult to stereoscopically view such an object. In the Galilean type optical system, however, the light beam emitted from a point on an object to be examined can be made into a parallel light beam by an objective and therefore, magnification change including that of the zoom optical system becomes simple. Also, there is a merit that various additional mechanisms can be mounted by inserting a beam splitter into the parallel light beam portion.
Japanese Utility Model Publication No. 19530 1983 and Japanese Laid-Open Patent Application No. 31992/1979 are known as the Galilean type optical systems improved so as to have a convergence angle.
The former has wedge prisms provided rearwardly of eyepieces, and the latter has prisms provided forwardly of eyepieces. Both of these have a disadvantage that the convergence angle changes when the adjustment of the eye width is effected. Furthermore, in the aforementioned Japanese Utility Model Publication No. 19530/1983, the wedge prisms provided rearwardly of eyepieces are close to the examiner's eyes, and this leads to a disadvantage that it is difficult for the examiner to see through the eyepieces.
Also, the natural line of vision of the human being has convergence and at the same time, looks somewhat downwardly when it sees a nearby object. Therefore, it is desired to provide an angle of depression to the observation optical axes to thereby reduce the fatigue of the examiner's eyes and facilitate the observation. However in these apparatuses, no consideration is given to the angle of depression.
Further, where a stereoscopic microscope of this type is used as a slit lamp or the like, in operation, the observer sees a region to be observed by the naked eye while keeping his eyes away from the stereoscopic microscope. Looking into the stereoscopic microscope is frequently repeated, but the observer need change his line of vision greatly when he sees the region to be observed while keeping his eyes away from the stereoscopic microscope. This is cumbersome to the observer.